Using a wide variety of experimental approaches we and other investigators have concluded that superhelical DNA contains altered or interrupted secondary structure. In the case of SV40 and polyoma DNA the evidence strongly supports the appearance of unpaired bases at localized sites. The major focus of our research program centers on the structural details and role of unpaired regions in biological function. The following are the objectives of our research program: An analysis of the role of the unpaired region in the in vitro transcription of SV40 DNA by E. coli RNA polymerase. Characterization of the chemical modification of superhelical SV40 DNA I with CMC carbodiimide. A more detailed mapping of the unpaired regions of SV40 by high specific activity carbodiimide binding coupled with enzymatic analysis, i.e., restriction endonucleases and exonuclease III analysis. The continuation of our structural studies of circular DNA by full exploration of chemical probes of secondary structure and the development of other chemical probes. The study of the functional capacity of chemically modified SV40 DNA in vivo. BIBLIOGRAPHIC REFERENCES: Woodworth-Gutai, M. and J. Lebowitz. 1976. Introduction of interrupted secondary structure in supercoiled DNA as a funtion of superhelix density: Consideration of hairpin structures in superhelical DNA. J. Virol. 18:195-204. Lebowitz, J., C.F. Garon, M. Chen, and N.P. Salzman. 1976. Chemical modification of simian virus DNA by reaction with a water-soluble carbodiimide. J. Virol. 18:205-219.